/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.libcore.io;

import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import android.util.Log;

/**
 * A cache that uses a bounded amount of space on a filesystem. Each cache entry
 * has a string key and a fixed number of values. Values are byte sequences,
 * accessible as streams or files. Each value must be between {@code 0} and
 * {@code Integer.MAX_VALUE} bytes in length.
 *
 * <p>
 * The cache stores its data in a directory on the filesystem. This directory
 * must be exclusive to the cache; the cache may delete or overwrite files from
 * its directory. It is an error for multiple processes to use the same cache
 * directory at the same time.
 *
 * <p>
 * This cache limits the number of bytes that it will store on the filesystem.
 * When the number of stored bytes exceeds the limit, the cache will remove
 * entries in the background until the limit is satisfied. The limit is not
 * strict: the cache may temporarily exceed it while waiting for files to be
 * deleted. The limit does not include filesystem overhead or the cache journal
 * so space-sensitive applications should set a conservative limit.
 *
 * <p>
 * Clients call {@link #edit} to create or update the values of an entry. An
 * entry may have only one editor at one time; if a value is not available to be
 * edited then {@link #edit} will return null.
 * <ul>
 * <li>When an entry is being <strong>created</strong> it is necessary to supply
 * a full set of values; the empty value should be used as a placeholder if
 * necessary.
 * <li>When an entry is being <strong>edited</strong>, it is not necessary to
 * supply data for every value; values default to their previous value.
 * </ul>
 * Every {@link #edit} call must be matched by a call to {@link Editor#commit}
 * or {@link Editor#abort}. Committing is atomic: a read observes the full set
 * of values as they were before or after the commit, but never a mix of values.
 *
 * <p>
 * Clients call {@link #get} to read a snapshot of an entry. The read will
 * observe the value at the time that {@link #get} was called. Updates and
 * removals after the call do not impact ongoing reads.
 *
 * <p>
 * This class is tolerant of some I/O errors. If files are missing from the
 * filesystem, the corresponding entries will be dropped from the cache. If an
 * error occurs while writing a cache value, the edit will fail silently.
 * Callers should handle other problems by catching {@code IOException} and
 * responding appropriately.
 */
public final class DiskLruCache implements Closeable {
	static final String TAG = "DiskLruCache";

	static final String JOURNAL_FILE = "journal";
	static final String JOURNAL_FILE_TMP = "journal.tmp";
	static final String MAGIC = "libcore.io.DiskLruCache";
	static final String VERSION_1 = "1";
	static final long ANY_SEQUENCE_NUMBER = -1;
	private static final String CLEAN = "CLEAN";
	private static final String DIRTY = "DIRTY";
	private static final String REMOVE = "REMOVE";
	private static final String READ = "READ";
	/*
	 * This cache uses a journal file named "journal". A typical journal file
	 * looks like this: libcore.io.DiskLruCache 1 100 2
	 * 
	 * CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054 DIRTY
	 * 335c4c6028171cfddfbaae1a9c313c52 CLEAN 335c4c6028171cfddfbaae1a9c313c52
	 * 3934 2342 REMOVE 335c4c6028171cfddfbaae1a9c313c52 DIRTY
	 * 1ab96a171faeeee38496d8b330771a7a CLEAN 1ab96a171faeeee38496d8b330771a7a
	 * 1600 234 READ 335c4c6028171cfddfbaae1a9c313c52 READ
	 * 3400330d1dfc7f3f7f4b8d4d803dfcf6
	 * 
	 * The first five lines of the journal form its header. They are the
	 * constant string "libcore.io.DiskLruCache", the disk cache's version, the
	 * application's version, the value count, and a blank line.
	 * 
	 * Each of the subsequent lines in the file is a record of the state of a
	 * cache entry. Each line contains space-separated values: a state, a key,
	 * and optional state-specific values. o DIRTY lines track that an entry is
	 * actively being created or updated. Every successful DIRTY action should
	 * be followed by a CLEAN or REMOVE action. DIRTY lines without a matching
	 * CLEAN or REMOVE indicate that temporary files may need to be deleted. o
	 * CLEAN lines track a cache entry that has been successfully published and
	 * may be read. A publish line is followed by the lengths of each of its
	 * values. o READ lines track accesses for LRU. o REMOVE lines track entries
	 * that have been deleted.
	 * 
	 * The journal file is appended to as cache operations occur. The journal
	 * may occasionally be compacted by dropping redundant lines. A temporary
	 * file named "journal.tmp" will be used during compaction; that file should
	 * be deleted if it exists when the cache is opened.
	 */
	private final File directory;
	private final File journalFile;
	private final File journalFileTmp;
	private final int appVersion;
	private final long maxSize;
	private final int valueCount;
	private long size = 0;
	private Writer journalWriter;
	private final LinkedHashMap<String, Entry> lruEntries = new LinkedHashMap<String, Entry>(0, 0.75f, true);
	private int redundantOpCount;
	/**
	 * To differentiate between old and current snapshots, each entry is given a
	 * sequence number each time an edit is committed. A snapshot is stale if
	 * its sequence number is not equal to its entry's sequence number.
	 */
	private long nextSequenceNumber = 0;
	/** This cache uses a single background thread to evict entries. */
	private final ExecutorService executorService = new ThreadPoolExecutor(0, 1, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
	private final Callable<Void> cleanupCallable = new Callable<Void>() {
		@Override
		public Void call() throws Exception {
			synchronized (DiskLruCache.this) {
				if (journalWriter == null) {
					return null; // closed
				}
				trimToSize();
				if (journalRebuildRequired()) {
					rebuildJournal();
					redundantOpCount = 0;
				}
			}
			return null;
		}
	};

	private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {
		this.directory = directory;
		this.appVersion = appVersion;
		this.journalFile = new File(directory, JOURNAL_FILE);
		this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);
		this.valueCount = valueCount;
		this.maxSize = maxSize;
	}

	/**
	 * Opens the cache in {@code directory}, creating a cache if none exists
	 * there.
	 *
	 * @param directory a writable directory
	 * @param appVersion
	 * @param valueCount the number of values per cache entry. Must be positive.
	 * @param maxSize the maximum number of bytes this cache should use to store
	 * @throws IOException if reading or writing the cache directory fails
	 */
	public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize) throws IOException {
		if (maxSize <= 0) {
			throw new IllegalArgumentException("maxSize <= 0");
		}
		if (valueCount <= 0) {
			throw new IllegalArgumentException("valueCount <= 0");
		}
		// prefer to pick up where we left off
		DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
		if (cache.journalFile.exists()) {
			try {
				cache.readJournal();
				cache.processJournal();
				cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true));
				return cache;
			} catch (IOException journalIsCorrupt) {
				Log.w(TAG, "DiskLruCache " + directory + " is corrupt: " + journalIsCorrupt.getMessage() + ", removing");
				cache.delete();
			}
		}
		// create a new empty cache
		directory.mkdirs();
		cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
		cache.rebuildJournal();
		return cache;
	}

	private void readJournal() throws IOException {
		StrictLineReader reader = new StrictLineReader(new FileInputStream(journalFile), Charsets.US_ASCII);
		try {
			String magic = reader.readLine();
			String version = reader.readLine();
			String appVersionString = reader.readLine();
			String valueCountString = reader.readLine();
			String blank = reader.readLine();
			if (!MAGIC.equals(magic) || !VERSION_1.equals(version) || !Integer.toString(appVersion).equals(appVersionString)
					|| !Integer.toString(valueCount).equals(valueCountString) || !"".equals(blank)) {
				throw new IOException("unexpected journal header: [" + magic + ", " + version + ", " + valueCountString + ", " + blank
						+ "]");
			}
			int lineCount = 0;
			while (true) {
				try {
					readJournalLine(reader.readLine());
					lineCount++;
				} catch (EOFException endOfJournal) {
					break;
				}
			}
			redundantOpCount = lineCount - lruEntries.size();
		} finally {
			IoUtils.closeQuietly(reader);
		}
	}

	private void readJournalLine(String line) throws IOException {
		int firstSpace = line.indexOf(' ');
		if (firstSpace == -1) {
			throw new IOException("unexpected journal line: " + line);
		}
		int keyBegin = firstSpace + 1;
		int secondSpace = line.indexOf(' ', keyBegin);
		final String key;
		if (secondSpace == -1) {
			key = line.substring(keyBegin);
			if (firstSpace == REMOVE.length() && line.startsWith(REMOVE)) {
				lruEntries.remove(key);
				return;
			}
		} else {
			key = line.substring(keyBegin, secondSpace);
		}
		Entry entry = lruEntries.get(key);
		if (entry == null) {
			entry = new Entry(key);
			lruEntries.put(key, entry);
		}
		if (secondSpace != -1 && firstSpace == CLEAN.length() && line.startsWith(CLEAN)) {
			String[] parts = line.substring(secondSpace + 1).split(" ");
			entry.readable = true;
			entry.currentEditor = null;
			entry.setLengths(parts);
		} else if (secondSpace == -1 && firstSpace == DIRTY.length() && line.startsWith(DIRTY)) {
			entry.currentEditor = new Editor(entry);
		} else if (secondSpace == -1 && firstSpace == READ.length() && line.startsWith(READ)) {
			// this work was already done by calling lruEntries.get()
		} else {
			throw new IOException("unexpected journal line: " + line);
		}
	}

	/**
	 * Computes the initial size and collects garbage as a part of opening the
	 * cache. Dirty entries are assumed to be inconsistent and will be deleted.
	 */
	private void processJournal() throws IOException {
		deleteIfExists(journalFileTmp);
		for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext();) {
			Entry entry = i.next();
			if (entry.currentEditor == null) {
				for (int t = 0; t < valueCount; t++) {
					size += entry.lengths[t];
				}
			} else {
				entry.currentEditor = null;
				for (int t = 0; t < valueCount; t++) {
					deleteIfExists(entry.getCleanFile(t));
					deleteIfExists(entry.getDirtyFile(t));
				}
				i.remove();
			}
		}
	}

	/**
	 * Creates a new journal that omits redundant information. This replaces the
	 * current journal if it exists.
	 */
	private synchronized void rebuildJournal() throws IOException {
		if (journalWriter != null) {
			journalWriter.close();
		}
		Writer writer = new BufferedWriter(new FileWriter(journalFileTmp));
		writer.write(MAGIC);
		writer.write("\n");
		writer.write(VERSION_1);
		writer.write("\n");
		writer.write(Integer.toString(appVersion));
		writer.write("\n");
		writer.write(Integer.toString(valueCount));
		writer.write("\n");
		writer.write("\n");
		for (Entry entry : lruEntries.values()) {
			if (entry.currentEditor != null) {
				writer.write(DIRTY + ' ' + entry.key + '\n');
			} else {
				writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
			}
		}
		writer.close();
		journalFileTmp.renameTo(journalFile);
		journalWriter = new BufferedWriter(new FileWriter(journalFile, true));
	}

	private static void deleteIfExists(File file) throws IOException {
		/*
		 * try { Libcore.os.remove(file.getPath()); } catch (ErrnoException
		 * errnoException) { if (errnoException.errno != OsConstants.ENOENT) {
		 * throw new IOException(); } }
		 */
		if (file.exists() && !file.delete()) {
			throw new IOException();
		}
	}

	/**
	 * Returns a snapshot of the entry named {@code key}, or null if it doesn't
	 * exist is not currently readable. If a value is returned, it is moved to
	 * the head of the LRU queue.
	 */
	public synchronized Snapshot get(String key) throws IOException {
		checkNotClosed();
		validateKey(key);
		Entry entry = lruEntries.get(key);
		if (entry == null) {
			return null;
		}
		if (!entry.readable) {
			return null;
		}
		/*
		 * Open all streams eagerly to guarantee that we see a single published
		 * snapshot. If we opened streams lazily then the streams could come
		 * from different edits.
		 */
		InputStream[] ins = new InputStream[valueCount];
		try {
			for (int i = 0; i < valueCount; i++) {
				ins[i] = new FileInputStream(entry.getCleanFile(i));
			}
		} catch (FileNotFoundException e) {
			// a file must have been deleted manually!
			return null;
		}
		redundantOpCount++;
		journalWriter.append(READ + ' ' + key + '\n');
		if (journalRebuildRequired()) {
			executorService.submit(cleanupCallable);
		}
		return new Snapshot(key, entry.sequenceNumber, ins);
	}

	/**
	 * Returns an editor for the entry named {@code key}, or null if another
	 * edit is in progress.
	 */
	public Editor edit(String key) throws IOException {
		return edit(key, ANY_SEQUENCE_NUMBER);
	}

	private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {
		checkNotClosed();
		validateKey(key);
		Entry entry = lruEntries.get(key);
		if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {
			return null; // snapshot is stale
		}
		if (entry == null) {
			entry = new Entry(key);
			lruEntries.put(key, entry);
		} else if (entry.currentEditor != null) {
			return null; // another edit is in progress
		}
		Editor editor = new Editor(entry);
		entry.currentEditor = editor;
		// flush the journal before creating files to prevent file leaks
		journalWriter.write(DIRTY + ' ' + key + '\n');
		journalWriter.flush();
		return editor;
	}

	/**
	 * Returns the directory where this cache stores its data.
	 */
	public File getDirectory() {
		return directory;
	}

	/**
	 * Returns the maximum number of bytes that this cache should use to store
	 * its data.
	 */
	public long maxSize() {
		return maxSize;
	}

	/**
	 * Returns the number of bytes currently being used to store the values in
	 * this cache. This may be greater than the max size if a background
	 * deletion is pending.
	 */
	public synchronized long size() {
		return size;
	}

	private synchronized void completeEdit(Editor editor, boolean success) throws IOException {
		Entry entry = editor.entry;
		if (entry.currentEditor != editor) {
			throw new IllegalStateException();
		}
		// if this edit is creating the entry for the first time, every index
		// must have a value
		if (success && !entry.readable) {
			for (int i = 0; i < valueCount; i++) {
				if (!editor.written[i]) {
					editor.abort();
					throw new IllegalStateException("Newly created entry didn't create value for index " + i);
				}
				if (!entry.getDirtyFile(i).exists()) {
					editor.abort();
					Log.w(TAG, "DiskLruCache: Newly created entry doesn't have file for index " + i);
					return;
				}
			}
		}
		for (int i = 0; i < valueCount; i++) {
			File dirty = entry.getDirtyFile(i);
			if (success) {
				if (dirty.exists()) {
					File clean = entry.getCleanFile(i);
					dirty.renameTo(clean);
					long oldLength = entry.lengths[i];
					long newLength = clean.length();
					entry.lengths[i] = newLength;
					size = size - oldLength + newLength;
				}
			} else {
				deleteIfExists(dirty);
			}
		}
		redundantOpCount++;
		entry.currentEditor = null;
		if (entry.readable | success) {
			entry.readable = true;
			journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
			if (success) {
				entry.sequenceNumber = nextSequenceNumber++;
			}
		} else {
			lruEntries.remove(entry.key);
			journalWriter.write(REMOVE + ' ' + entry.key + '\n');
		}
		if (size > maxSize || journalRebuildRequired()) {
			executorService.submit(cleanupCallable);
		}
	}

	/**
	 * We only rebuild the journal when it will halve the size of the journal
	 * and eliminate at least 2000 ops.
	 */
	private boolean journalRebuildRequired() {
		final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;
		return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD && redundantOpCount >= lruEntries.size();
	}

	/**
	 * Drops the entry for {@code key} if it exists and can be removed. Entries
	 * actively being edited cannot be removed.
	 *
	 * @return true if an entry was removed.
	 */
	public synchronized boolean remove(String key) throws IOException {
		checkNotClosed();
		validateKey(key);
		Entry entry = lruEntries.get(key);
		if (entry == null || entry.currentEditor != null) {
			return false;
		}
		for (int i = 0; i < valueCount; i++) {
			File file = entry.getCleanFile(i);
			if (!file.delete()) {
				throw new IOException("failed to delete " + file);
			}
			size -= entry.lengths[i];
			entry.lengths[i] = 0;
		}
		redundantOpCount++;
		journalWriter.append(REMOVE + ' ' + key + '\n');
		lruEntries.remove(key);
		if (journalRebuildRequired()) {
			executorService.submit(cleanupCallable);
		}
		return true;
	}

	/**
	 * Returns true if this cache has been closed.
	 */
	public boolean isClosed() {
		return journalWriter == null;
	}

	private void checkNotClosed() {
		if (journalWriter == null) {
			throw new IllegalStateException("cache is closed");
		}
	}

	/**
	 * Force buffered operations to the filesystem.
	 */
	public synchronized void flush() throws IOException {
		checkNotClosed();
		trimToSize();
		journalWriter.flush();
	}

	/**
	 * Closes this cache. Stored values will remain on the filesystem.
	 */
	public synchronized void close() throws IOException {
		if (journalWriter == null) {
			return; // already closed
		}
		for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {
			if (entry.currentEditor != null) {
				entry.currentEditor.abort();
			}
		}
		trimToSize();
		journalWriter.close();
		journalWriter = null;
	}

	private void trimToSize() throws IOException {
		while (size > maxSize) {
			// Map.Entry<String, Entry> toEvict = lruEntries.eldest();
			final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();
			remove(toEvict.getKey());
		}
	}

	/**
	 * Closes the cache and deletes all of its stored values. This will delete
	 * all files in the cache directory including files that weren't created by
	 * the cache.
	 */
	public void delete() throws IOException {
		close();
		IoUtils.deleteContents(directory);
	}

	private void validateKey(String key) {
		if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {
			throw new IllegalArgumentException("keys must not contain spaces or newlines: \"" + key + "\"");
		}
	}

	private static String inputStreamToString(InputStream in) throws IOException {
		return Streams.readFully(new InputStreamReader(in, Charsets.UTF_8));
	}

	/**
	 * A snapshot of the values for an entry.
	 */
	public final class Snapshot implements Closeable {
		private final String key;
		private final long sequenceNumber;
		private final InputStream[] ins;

		private Snapshot(String key, long sequenceNumber, InputStream[] ins) {
			this.key = key;
			this.sequenceNumber = sequenceNumber;
			this.ins = ins;
		}

		/**
		 * Returns an editor for this snapshot's entry, or null if either the
		 * entry has changed since this snapshot was created or if another edit
		 * is in progress.
		 */
		public Editor edit() throws IOException {
			return DiskLruCache.this.edit(key, sequenceNumber);
		}

		/**
		 * Returns the unbuffered stream with the value for {@code index}.
		 */
		public InputStream getInputStream(int index) {
			return ins[index];
		}

		/**
		 * Returns the string value for {@code index}.
		 */
		public String getString(int index) throws IOException {
			return inputStreamToString(getInputStream(index));
		}

		@Override
		public void close() {
			for (InputStream in : ins) {
				IoUtils.closeQuietly(in);
			}
		}
	}

	/**
	 * Edits the values for an entry.
	 */
	public final class Editor {
		private final Entry entry;
		private final boolean[] written;
		private boolean hasErrors;

		private Editor(Entry entry) {
			this.entry = entry;
			this.written = (entry.readable) ? null : new boolean[valueCount];
		}

		/**
		 * Returns an unbuffered input stream to read the last committed value,
		 * or null if no value has been committed.
		 */
		public InputStream newInputStream(int index) throws IOException {
			synchronized (DiskLruCache.this) {
				if (entry.currentEditor != this) {
					throw new IllegalStateException();
				}
				if (!entry.readable) {
					return null;
				}
				return new FileInputStream(entry.getCleanFile(index));
			}
		}

		/**
		 * Returns the last committed value as a string, or null if no value has
		 * been committed.
		 */
		public String getString(int index) throws IOException {
			InputStream in = newInputStream(index);
			return in != null ? inputStreamToString(in) : null;
		}

		/**
		 * Returns a new unbuffered output stream to write the value at
		 * {@code index}. If the underlying output stream encounters errors when
		 * writing to the filesystem, this edit will be aborted when
		 * {@link #commit} is called. The returned output stream does not throw
		 * IOExceptions.
		 */
		public OutputStream newOutputStream(int index) throws IOException {
			synchronized (DiskLruCache.this) {
				if (entry.currentEditor != this) {
					throw new IllegalStateException();
				}
				if (!entry.readable) {
					written[index] = true;
				}
				return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));
			}
		}

		/**
		 * Sets the value at {@code index} to {@code value}.
		 */
		public void set(int index, String value) throws IOException {
			Writer writer = null;
			try {
				writer = new OutputStreamWriter(newOutputStream(index), Charsets.UTF_8);
				writer.write(value);
			} finally {
				IoUtils.closeQuietly(writer);
			}
		}

		/**
		 * Commits this edit so it is visible to readers. This releases the edit
		 * lock so another edit may be started on the same key.
		 */
		public void commit() throws IOException {
			if (hasErrors) {
				completeEdit(this, false);
				remove(entry.key); // the previous entry is stale
			} else {
				completeEdit(this, true);
			}
		}

		/**
		 * Aborts this edit. This releases the edit lock so another edit may be
		 * started on the same key.
		 */
		public void abort() throws IOException {
			completeEdit(this, false);
		}

		private class FaultHidingOutputStream extends FilterOutputStream {
			private FaultHidingOutputStream(OutputStream out) {
				super(out);
			}

			@Override
			public void write(int oneByte) {
				try {
					out.write(oneByte);
				} catch (IOException e) {
					hasErrors = true;
				}
			}

			@Override
			public void write(byte[] buffer, int offset, int length) {
				try {
					out.write(buffer, offset, length);
				} catch (IOException e) {
					hasErrors = true;
				}
			}

			@Override
			public void close() {
				try {
					out.close();
				} catch (IOException e) {
					hasErrors = true;
				}
			}

			@Override
			public void flush() {
				try {
					out.flush();
				} catch (IOException e) {
					hasErrors = true;
				}
			}
		}
	}

	private final class Entry {
		private final String key;
		/** Lengths of this entry's files. */
		private final long[] lengths;
		/** True if this entry has ever been published */
		private boolean readable;
		/** The ongoing edit or null if this entry is not being edited. */
		private Editor currentEditor;
		/**
		 * The sequence number of the most recently committed edit to this
		 * entry.
		 */
		private long sequenceNumber;

		private Entry(String key) {
			this.key = key;
			this.lengths = new long[valueCount];
		}

		public String getLengths() throws IOException {
			StringBuilder result = new StringBuilder();
			for (long size : lengths) {
				result.append(' ').append(size);
			}
			return result.toString();
		}

		/**
		 * Set lengths using decimal numbers like "10123".
		 */
		private void setLengths(String[] strings) throws IOException {
			if (strings.length != valueCount) {
				throw invalidLengths(strings);
			}
			try {
				for (int i = 0; i < strings.length; i++) {
					lengths[i] = Long.parseLong(strings[i]);
				}
			} catch (NumberFormatException e) {
				throw invalidLengths(strings);
			}
		}

		private IOException invalidLengths(String[] strings) throws IOException {
			throw new IOException("unexpected journal line: " + Arrays.toString(strings));
		}

		public File getCleanFile(int i) {
			return new File(directory, key + "." + i);
		}

		public File getDirtyFile(int i) {
			return new File(directory, key + "." + i + ".tmp");
		}
	}
}